Chemistry Reference
In-Depth Information
4.2.1 Carbonaceous Matter
Incomplete combustion of biomass is known to produce particulate carbonaceous
components, organic matter, and black carbon [
42
]. The concentration of OM
increases significantly during the LRT smoke episodes. During the major episode
in spring 2006, the observed OM concentrations were elevated by a factor of 8 in
Helsinki (Fig.
2
;[
19
]), factor of 5-11 in Sweden [
25
], and around tenfold at
Spitsbergen [
10
]. The concentration of OM increased more than that of PM
resulting in a larger fraction of organic matter in PM during the smokes. For
example in Helsinki, the contribution of OM to PM
2.5
doubled from the reference
period to the episodes [
19
].
Smoke episodes have no clear effect on the general water solubility of organic
matter. In Helsinki in 2006, the water solubility of OM did not change significantly
from the reference period to the LRT smoke episodes [
19
]. Some water-soluble
organic compound groups were more pronounced in the smoke samples. Dicarbox-
ylic acids (succinic, malonic, and oxalic acids) were found in the smoke samples
collected in August to September 2002 in Helsinki [
14
]. Dicarboxylic acid
concentrations were elevated both in the fine and coarse fraction suggesting that
the acids were probably condensed onto existing particles. Especially oxalic acid
has been associated with the biomass smoke particles [
19
] but there are several
other sources for it. Also elevated concentrations of PAHs have been attributed to
the smoke episodes [
22
,
23
]. Individual particle analysis revealed that during the
LRT smoke episode in spring 2004 in Hyyti
a there were particles called as tar
balls, a distinct carbonaceous particle type from soot [
17
]. Tar balls originated from
biomass burning, especially during smoldering conditions.
Monosaccharide anhydrides are unique organic tracer compounds for biomass
burning. For example in 2006 in Helsinki, levoglucosan concentrations were
18 times higher during the plumes than in the reference period (Fig.
2
;[
18
]).
Usually the separation of LRT smoke from the local biomass combustion is
challenging. Using the fractions of levoglucosan, mannosan, and galactosan in
the total amount of MAs, LRT smoke episodes were distinguished from the local
wood burning [
38
]. The proportions of MAs are different from one type of burnt
biomass to the other. The ratio of levoglucosan to galactosan was lower during the
LRT smoke plumes in April to May and in August 2006 than in the period with
residential wood combustion. That was assumed to be caused partly by the burning
of foliar material in wildfires and logs in residential combustion.
Smoke particles contain black carbon but the concentrations are lower than for
organic matter. For example in spring 2006 in Sweden, the concentration of OC
rose more significantly than that of BC resulting in lower BC/OC ratios during the
smoke episodes than in the reference period [
25
]. In 2010 in Kuopio, black carbon
concentrations increased around 12 times during the smoke episodes but the
fraction of BC in PM
2.5
remained nearly the same [
33
]. In some studies similar
material to black carbon has also been measured as elemental carbon, light absorb-
ing carbon, black smoke, or equivalent black carbon depending on the measurement
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